With the development of the display technology, flat display devices such as a liquid crystal display (LCD) are widely employed in various consumer electronics like a mobile phone, a television, personal digital assistance, a digital camera, a laptop, a desktop computer, locating in the mainstream of display devices.
Most of liquid crystal display devices on the market are backlight liquid crystal displays, including liquid crystal display panels and backlight modules. The operational principle of a liquid crystal display panel is to dispose liquid crystal molecules on two parallel glass substrates, a number of vertical and horizontal weak currents are between the two glass substrates, which can control the liquid crystal molecules to redirect by power on/off, light from the backlight module can be refracted to show images.
A liquid crystal display panel can consist of a color filter (CF) substrate, a thin film transistor (TFT) substrate, a liquid crystal (LC) between the color filter substrate and the thin film transistor substrate, and a sealant.
A layer of thin film material is disposed on the CF substrate and the TFT substrate of a liquid crystal display respectively, mainly for aligning liquid crystal molecules, which is referred to as an alignment film (mostly a polyimide (PI) material). The main component of the alignment film is an abrasion alignment PI material or a light alignment PI material, both of which have their own drawbacks. First, the friction alignment PI material can cause problems like dust particles, static electricity residue, brushing streak, which can reduce yield of the product, though the light alignment PI material can avoid the problems above, heat resistance, ageing resistance and LC molecules anchorage are poor due to the property of material, affecting quality of a panel; second, PI materials have strong polarity and hygroscopicity, alignment can be inconsistent after storage and transportation, and the price of PI materials is high, a process of filming on a TFT-LCD is complicated, resulting in increasing costs of a panel. If alignment of liquid crystal molecules can be achieved without a PI film, costs of a panel can be reduced significantly.